Machinery powered by electric motors or internal combustion engines (typically referred to as "prime movers") often use gears, shafts and the like to form what is referred to a drive train providing power to perform an end-use function. Automobiles, metal cutting and shaping machines, toggle-type presses and construction and earth-moving machines are but a few examples of such machinery.
As more specific examples, such machinery drive trains uses gears and shafts in speed reducers to reduce speed (from that of the motor or engine output shaft) and increase torque and/or to change the direction of power flow. Shafts interconnect "stages" of gearing or connect a final gearing stage to an output device such as automobile wheels, press head or, in the case of an earth-moving machine known as a walking dragline, to a "walk leg" drive.
In such machines, the drive train components (gears, shafts and the like) range in size from a few pounds to several thousand pounds. Another characteristic of certain types of machines, e.g., toggle presses and walking draglines, is that certain machine functions tend to load (and wear) drive train components unevenly. For example, the drive train of a toggle press (especially that portion driving the toggle press head mechanism) is most heavily loaded over only that fraction of a revolution relating to the final, piece-forming part of the press stroke. In a walking dragline, the walk leg drive is most heavily loaded only during that part of a revolution, nominally about 120.degree. or less, during which the dragline is being lifted to take a "step."
To keep the machine functioning efficiently and in condition to satisfactory perform its task, worn parts need to be replaced or repaired. However, with larger machines, maintenance and parts replacement can be an imposing challenge, especially if the parts are large and unwieldly. And the problem of repair and replacement is often aggravated in that access to gear train parts is obstructed. There may be other machine components which, unless major parts of the machine are dismantled, prevent access to such parts along any direction except through a relatively small open spatial area. Nowhere is this more true than in large mobile machines such as earth-moving and earth-excavating machinery.
Such machinery is available in a wide variety of types ranging from the familiar rubber-tire mounted and crawler-mounted to the less-common dragline and the invention is described in connection with an exemplary dragline.
A dragline is often used for removing top soil and "overburden" to expose a valuable mineral, e.g., coal, beneath but near the earth's surface. Draglines are equipped with an angularly-extending boom from which is suspended a "bucket" having an open mouth and digging teeth, both pointing toward the main portion of the machine.
Overburden is removed by placing the bucket on the ground at a point distant from the machine and pulling it toward the machine, filling the bucket in the process. Once filled, the machine pivots about a central axis and the bucket emptied at a spoil pile somewhat away from the area being excavated.
Smaller draglines are crawler mounted (much like a military tank) and capable of movement in the same way albeit at much slower speeds. However, as draglines (and their digging buckets) increased in size, crawler mounting was found to be impractical and in the early 1900's, the "walking" dragline was developed. The walking dragline is so named because it takes short "steps" and uses a "walk leg" mechanism (which resembles a human leg) to do so. A difference is that in a walking dragline, both legs step simultaneously.
To give some perspective to the following discussion, an exemplary large walking dragline----made by Harnischfeger Industries of Milwaukee, Wis.----has a main housing portion (including the machinery deck, operator's cab and the like) which is about 105 feet long, about 80 feet wide, about 40 feet high and weighs about nine million pounds. The boom extends about 300 feet and the capacity of the digging bucket is about 80 cubic yards. The walk legs of such dragline take steps about seven feet in length. For reasons that will become apparent, the arrangement of such exemplary dragline prohibits access, except by major disassembly, to certain components of the walkleg mechanism.
An invention facilitating expedited, relatively easy repair of a drive train component having a region through which access to the component is obstructed would be an important advance in the art.